The Stellarium Dev Team - (Open Source)
Stellarium provides you with accurate data about the night sky, which can be used by professional and amateur astronomers alike. Basically it's a planetarium for your computer. The application shows a realistic sky in 3D; the same as what you'd see with a telescope.
Key features include:
Stellarium has a great looking interface that can be accessed by all levels of user. It comes with a powerful zoom feature, time control, fish-eye projection for planetarium domes, extensive keyboard control and telescope control. Stellarium also comes with plugin control, so you can add functions like artificial satellites, ocular simulation, and telescope configuration. You can also add to your database, new solar system objects from online resources.